Band Tails And Defect Density In P-type Doped Hydrogenated Amorphous Germanium

The correlations between the defect density, N D, Fermi energy, E F, and Urbach tail, E 0, are examined for rf-sputtered a-Ge:H films p-type doped by aluminum, gallium and indium. Photothermal deflection spectroscopy was used for the determination of N D and E 0, while E F was deduced from conductivity measurements. The present data show different dependence of N D on E F for samples doped by different dopants, but a similar behavior when N D is plotted as a function of E 0 or the solid-state dopant impurity concentration. The simple equilibrium model of doping alone is unable to explain the present results. The data suggest that the doping-induced defects observed are related to the large fraction of neutral dopant impurities expected to be present in the material.198-200PART 1399402Street, R.A., (1982) Phys. Rev. Lett., 49, p. 1187Winer, K., (1990) Phys. Rev., B41, p. 12150Pierz, K., Fuhs, W., Mell, H., (1991) Philos. Mag., B63, p. 123Ebersberger, B., Krühler, W., Fuhs, W., Mell, H., (1994) Appl. Phys. Lett., 65, p. 1683Comedi, D., Fajardo, F., Chambouleyron, I., (1995) Phys. Rev., B52, p. 4974Fajardo, F., Chambouleyron, I., (1995) Phys. Rev., B52, p. 4965Graeff, C.F.O., Stutzmann, M., Eberhardt, K., (1994) Philos. Mag., B69, p. 387Comedi, D., Fajardo, F., Chambouleyron, I., Tabacniks, M., (1994) J. Vac. Sci. Technol., A12, p. 3149Stutzmann, M., (1989) Philos Mag., B60, p. 531Aljishi, S., Shu, J., Ley, L., (1989) Mater. Res. Soc. Symp. Proc., 149, p. 12